Java to Kotlin converter: better and more correct code

j2k/src/org/jetbrains/jet/j2k/Utils.kt

@@ -136,3 +136,6 @@ fun PsiModifierListOwner.accessModifier(): String = when {
 }
 
 fun PsiMethod.isMainMethod(): Boolean = PsiMethodUtil.isMainMethod(this)
+
+fun <T: Any> List<T>.singleOrNull2(): T? = if (size == 1) this[0] else null
+fun <T: Any> Array<T>.singleOrNull2(): T? = if (size == 1) this[0] else null

j2k/src/org/jetbrains/jet/j2k/visitors/StatementVisitor.kt

@@ -24,6 +24,7 @@ import java.util.ArrayList
 import org.jetbrains.jet.j2k.hasWriteAccesses
 import org.jetbrains.jet.j2k.isInSingleLine
 import com.intellij.psi.tree.IElementType
+import org.jetbrains.jet.j2k.singleOrNull2
 
 open class StatementVisitor(public val converter: Converter) : JavaElementVisitor() {
     public var result: Statement = Statement.Empty
@@ -102,12 +103,11 @@ open class StatementVisitor(public val converter: Converter) : JavaElementVisito
         val condition = statement.getCondition()
         val body = statement.getBody()
 
-        if (initialization is PsiDeclarationStatement && initialization.getFirstChild()!!.getNextSibling() == null) {
-            val loopVar = initialization.getFirstChild() as? PsiLocalVariable
+        if (initialization is PsiDeclarationStatement) {
+            val loopVar = initialization.getDeclaredElements().singleOrNull2() as? PsiLocalVariable
             if (loopVar != null
                     && !loopVar.hasWriteAccesses(body)
                     && !loopVar.hasWriteAccesses(condition)
-                    && loopVar.countWriteAccesses(update) == 1
                     && condition is PsiBinaryExpression) {
                 val operationTokenType = condition.getOperationTokenType()
                 val lowerBound = condition.getLOperand()
@@ -117,10 +117,8 @@ open class StatementVisitor(public val converter: Converter) : JavaElementVisito
                         lowerBound.resolve() == loopVar &&
                         upperBound != null) {
                     val start = loopVar.getInitializer()
-                    if (start != null
-                            && update != null
-                            && update.getChildren().size == 1
-                            && update.getChildren().single().isPlusPlusExpression()) {
+                    if (start != null &&
+                            (update as? PsiExpressionStatement)?.getExpression()?.isVariablePlusPlus(loopVar) ?: false) {
                         val range = forIterationRange(start, upperBound, operationTokenType).assignNoPrototype()
                         val explicitType = if (converter.settings.specifyLocalVariableTypeByDefault) PrimitiveType(Identifier("Int").assignNoPrototype()).assignNoPrototype() else null
                         result = ForeachStatement(loopVar.declarationIdentifier(), explicitType, range, convertStatementOrBlock(body), statement.isInSingleLine())
@@ -173,6 +171,16 @@ open class StatementVisitor(public val converter: Converter) : JavaElementVisito
         }
     }
 
+    private fun PsiElement.isVariablePlusPlus(variable: PsiVariable): Boolean {
+        //TODO: simplify code when KT-5453 fixed
+        val pair = when (this) {
+            is PsiPostfixExpression -> getOperationTokenType() to getOperand()
+            is PsiPrefixExpression -> getOperationTokenType() to getOperand()
+            else -> return false
+        }
+        return pair.first == JavaTokenType.PLUSPLUS && (pair.second as? PsiReferenceExpression)?.resolve() == variable
+    }
+
     private fun forIterationRange(start: PsiExpression, upperBound: PsiExpression, comparisonTokenType: IElementType): Expression {
         if (start is PsiLiteralExpression
                 && start.getValue() == 0
@@ -337,11 +345,6 @@ open class StatementVisitor(public val converter: Converter) : JavaElementVisito
         result = Statement.Empty
     }
 
-    private fun PsiElement.isPlusPlusExpression(): Boolean {
-        return (this is PsiPostfixExpression && this.getOperationTokenType() == JavaTokenType.PLUSPLUS) ||
-                (this is PsiPrefixExpression && this.getOperationTokenType() == JavaTokenType.PLUSPLUS)
-    }
-
     private fun convertStatementOrBlock(statement: PsiStatement?): Statement {
         return if (statement is PsiBlockStatement)
             converter.convertBlock(statement.getCodeBlock())

j2k/src/org/jetbrains/jet/j2k/visitors/SwitchConverter.kt

@@ -20,6 +20,7 @@ import com.intellij.psi.*
 import org.jetbrains.jet.j2k.ast.*
 import org.jetbrains.jet.j2k.Converter
 import java.util.ArrayList
+import org.jetbrains.jet.j2k.singleOrNull2
 
 class SwitchConverter(private val converter: Converter) {
     public fun convert(statement: PsiSwitchStatement): WhenStatement
@@ -113,6 +114,4 @@ class SwitchConverter(private val converter: Converter) {
     }
 
     private fun isSwitchBreak(statement: PsiStatement) = statement is PsiBreakStatement && statement.getLabelIdentifier() == null
-
-    private fun <T: Any> List<T>.singleOrNull2(): T? = if (size == 1) this[0] else null
 }